PROJECT SUMMARY Poor self-regulation (SR) skills are linked to detrimental health outcomes and disproportionately affect low- income children. Yet, not all children who grow up in poverty exhibit poor SR skills. Little is known about what factors delineate pathways associated with poor versus adaptive SR skills, which also limits our ability to identify who may benefit the most from targeted SR interventions. Children's biological sensitivity to context, or the degree to which they are susceptible to environmental influences, may be one such factor. Cortisol, a marker of hypothalamic-pituitary-adrenal (HPA) activity, is thought to reflect biological sensitivity and is consistently related to early adversity. Yet, the nature of the association between adversity, cortisol, and SR is not clear, as both higher and lower cortisol production in response to stress have been associated with SR. Furthermore, research linking early adversity, cortisol, and SR has focused on early childhood, despite dramatic changes in SR later in childhood that coincide with increasing academic and social demands. Finally, to our knowledge, no study has investigated the extent to which cortisol measured in early childhood could moderate response to SR-focused interventions in middle childhood. The proposed study will address this gap by using data from an existing longitudinal cohort of Dr. Miller's (n=275; R01DK098983; UH2HD087979; R21DK090718; RC1DK086376) to test hypotheses that early stress biology not only moderates the association between early adversity and poor SR, but also the extent of improvement in SR following an intervention delivered later in childhood. The specific aims of the study are, in a sample of low-income children: Aim 1: Test the hypothesis that cortisol moderates concurrent associations between early adversity and SR skills in early childhood. Aim 2: Test the hypothesis that cortisol moderates longitudinal associations between early adversity and SR skills in middle childhood. Aim 3: Test the hypothesis that children with moderate cortisol levels in early childhood exhibit greater improvement in SR skills following an intervention delivered in late childhood. In addition to these research aims, Dr. Lo will learn about the latest childhood SR intervention approaches, community-based program evaluation, implementation science, and the science of behavior change in order to design SR intervention studies with low-income children. She will be trained in sophisticated experimental designs and analytic techniques for optimizing behavioral interventions, as well as cortisol methodology and data analysis. The research and training aims proposed here will facilitate Dr. Lo's development as an independent scientist with a program of research dedicated to understanding the synergistic effects of early adversity and biological sensitivity on the development of SR, and evaluating efforts to promote SR growth.